The dependence of the electrical characteristics of the GaN epitaxial layer on the thermal treatment of the GaN buffer layer

Abstract

The GaN buffer layer was grown on the sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) at 525 °C. The following 1.3 μm epitaxial GaN growth was carried out at 1025 °C. We varied the ramping rate from 12.5 to 100 °C/min to study the quality of the epitaxial GaN. It has been found that the x-ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 °C/min. The maximum mobility is 435 cm2/V s at carrier concentration of 1.7×1017 cm−3. The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 °C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer.

Trade-off between thickness and temperature ramping rate of GaN buffer layer studied for high quality GaN growth on GaAs (1 1 1)A substrate

“…Therefore, obtaining a high-quality GaN layer in hot-wall epitaxy requires a trade-off between the thickness and the temperature ramping rate of the GaN buffer layer. Because of similarities between our results here and results obtained for growth on sapphire substrates [11][12][13], the crystalline quality of GaN layers grown on sapphire might also be dominated by the ratio of single-crystal (nano-crystallite) regions to amorphous-like matrix regions in the predeposited GaN buffer layer. Also, in the case of MOVPE, in which the temperature ramping rate of the buffer layer is much higher than that for HVPE, the use of a thinner buffer layer (20-30 nm) or annealing at a higher temperature for several minutes may needed to obtain a higher quality epitaxial layer [12].…”

Using optical reflectance to measure GaN nucleation layer decomposition kinetics

“…These changes include loss of material [4], reincorporation of gas phase atoms into the developing nuclei [5], improvements in the NL crystalline quality [6], and an increase in roughness [7]. By varying the annealing schedule [8,9] and environment as shown here, the NL decomposition kinetics and subsequent NL evolution can be significantly altered.…”

Understanding GaN nucleation layer evolution on sapphire

“…Changes in the NL growth parameters such as thickness [8,[12][13][14][15], growth T [16][17][18], growth rate [19][20][21], annealing schedule from low to high T [13,[22][23][24], and extent to which the sapphire surface is exposed to NH 3 prior to NL growth [15,17,25] have all been shown to influence the NL growth and subsequent quality of the high-T GaN layers.…”